Surfacing machinery is used to perform surface operations on workpieces, for example, to sand or plane lumber, planks, panels, etc. Such surfacing machinery typically includes upper and lower heads for cutting or sanding the workpieces, and a feed assembly for advancing the workpiece through the heads. The feed assembly preferably provides a self-centering effect so that whatever amount of material is being removed, one-half will be removed from each side, thereby maximizing yield.
Self-centering feed assemblies for abrasive grinding machines are disclosed in U.S. Pat. No. 4,322,919 issued to Gerber on Apr. 6, 1982 and in U.S. Pat. No. 4,640,056 issued to Stump on Feb. 3, 1987, both of which are herein incorporated by reference. These prior art feed assemblies allowed each workpiece to float or center at the sanding head position and to thereby achieve equal stock removal on each side of each board. Because the abrasive belt heads themselves had a self-centering effect, these feed assemblies were required to provide the necessary horizontal forces required to feed each board, but follow the surface of each board so as to not interfere with the centering effect at the abrasive belt heads.
However, when used in connection with cutting heads, as opposed to sanding or grinding heads, these prior art feed assemblies were not adequate to achieve the desired individual centering result, since the cutting heads do not provide a self-centering effect. This is due to the fact that when using cutting heads instead of abrasive heads, the vertical forces on the workpiece are exactly the opposite, as a cutting head tries to pull the board into the cutter, whereas an abrasive head tries to push the board away from the abrasive belt. As a result, the cutting heads would remove an unequal amount from each side and tend to gouge or otherwise cut the workpiece unevenly, especially if the workpiece is uneven, warped or contains other variations. In an attempt to compensate for such problems, the cutting heads normally are displaced relative to each other, as opposed to the desired position of directly opposing each other, resulting in uneven stock removal from each side.
Accordingly, there is a need in a cutting head planer machine for a method and apparatus to adequately center and feed workpieces to the cutting head assembly so that an equal amount of material will be removed from both sides of each and every board independent of individual board thickness variations. The present invention fulfills such a need.